A. Field of the Invention
This invention relates to a process for improving tensile properties of aramid fibers and structurally related fibers by soaking the fibers in a tertiary amine (e.g. pyridine) maintained at a temperature of at least 80.degree. C.
The term "aramid" as used herein has its usual meaning which is "a manufactured fiber in which the fiberforming substance is a long-chain synthetic aromatic polyamide in which at least 85% of the amine linkages are attached directly to two aromatic linkages". The term "structurally related fibers" when used herein with reference to aramid fibers means a modified aramid fiber in which at least a portion of the amide linkages are replaced by hydrazide linkages ##STR1## R=H or C.sub.1 to C.sub.4 alkyl) and/or oxadiazole linkages ##STR2## The term "fiber" as used herein means a yarn composed of short fibers (staple) or one or more filaments.
B. Description of the Prior Art
Aramid fibers, such as those prepared from poly-(m-phenyleneisophthalamide) (i.e. MPD-I) have gained acceptance in recent years because of their excellent resistance to burning and their low generation of smoke when forced to burn, particularly, in applications such as garments for use by firemen, foundry workers, race car drivers, etc. and for drapes and carpets in hospitals and aboard ships and aircrafts. On the other hand, aramid fibers, such as those prepared from poly(p-phenylene terephthalamide) (i.e. PPD-T), and structurally related fibers such as, fibers of the polyterephthalamide of p-aminobenzhydrazide (i.e. BABH-T) and fibers of p-phenylene oxadiazole/p-phenylene N-methylhydrazide copolymer (i.e. OCH), have gained acceptance where high strength is desired, such as, for tire yarn and in composites. Even though aramid fibers have gained acceptance, nevertheless, there is a need to improve the tensile properties of these fibers. In the case of MPD-I type fibers there is a need to reduce its wide range of alongation-to-break values (Eb). A wide range of Eb values leads not only to shrinkage problems when fabrics made from the fibers are laundered, but also to pilling and fuzzing properties of such fabrics. In the case of PPD-T, BABH-T, and OCH fibers it would be desirable to further increase the tensile properties thereof and thereby provide yet a higher strength fiber and higher modulus fiber, especially, if this can be accomplished without loss of elongation-to-break, i.e., with preservation of toughness.
Accordingly, it is an object of the present invention to provide a simple, economical process for improving the tensile properties of aramid fibers and structurally related fibers.